The present invention relates to a device and a method for determining the properties of surfaces.
The quality of visible surfaces is a significant property of objects used in everyday life such as furnishings and consumer items such as cars and the like, thus decisively determining their overall impression on a human observer. An example therefor are high-gloss or metallic finishes of car bodies. The reproducible evaluation of the quality of surfaces in particular of said high-gloss finishes requires measuring instruments which capture precisely those physical quantities which decisively determine the overall impression on a human observer. Various methods and devices are known in the prior art for determining the visual properties and specifically the reflection characteristics of surfaces.
One drawback of these measuring devices is that they use substantially collimated light, i.e. directional parallel light beams for determining the reflection or diffusion characteristics of the object to be examined. On the one hand, such devices are capable of simulating the reflection characteristics for example of finished car body parts on cloudless days because then sunlight may be considered to be substantially collimated light.
However, finished surfaces in particular may also show properties whose overall impression will only become apparent to a human observer on overcast days because then the light will impinge on the surface to be examined from a plurality of directions, being scattered by the clouds i.e. uncollimated or diffused, respectively. Thus the problem is that the impression which the surface actually gives to a human observer results from the kind of illumination, i.e. whether the object is illuminated by collimated and/or uncollimated light or these types interact.